Right click on your connection from the Network Connections window and click 'Properties'.

Select 'Internet Protocol (TCP/IP)' and click 'Properties'.

Click the radio button Use the following DNS server addresses and type in Comodo Secure DNS addresses in the Preferred DNS server and Alternate DNS server fields.

Please note down your current DNS settings before switching to Comodo Secure DNS, in case you want to return to your old settings for any reason.

Preferred DNS server address for Comodo Secure DNS is: 8.26.56.26

Alternate DNS server address for Comodo Secure DNS is: 8.20.247.20

You can disable Comodo Secure DNS by:

Selecting 'Obtain DNS server address automatically'. This means that you will use the DNS server provided by your ISP. This is the option that most home users should choose if they wish to disable the service.